No man really becomes a fool until he stops asking questions.人若不再发问，就会变得愚蠢。 She did not leave the room until the child fell asleep. 直到孩子睡着后她才离开房间。 ③ It was not until...that?是个强调句式，that后用陈述句语序，不能用倒装形式。只有将Not until放在句首时，that后的句子才用倒装结构
It was not until he saw his mother that he realized how old she had become. 直到看见母亲，他才意识到母亲已经变老了。
It was not until I had read your letter that I understood the true state of affairs. 直到读了你的信，我才明白了事实的真相。
说明：? 主句为非持续动词的肯定式，只能用before,表示“先于”。
He applied three times before he was finally admitted to the university. ? 主句谓语为非持续动词否定式,until与before均可使用，但含义略有区别。
He didn't arrive home until I returned. 他直到我回来才到家。
He didn't arrive home before I returned. 在我回来之前他尚未到家。
since意为“自从?以来”，表示过去某个时间点开始一直延续到现在的一个 时段，since
后不能用否定词。since后用非持续性动词或持续性动词，及用什么时态，含义大不相同。
since的一般用法
① since从句用非持续性动词的一般过去时，表示主句（用现在完成时或现在完成进行时） 动作的起始点。意为“自从”。
Electricity has been widely used since it was discovered. 自从发现电以来，它得到了广泛应用。
I’ve been working here since I graduated from school. 从学校毕业后我就一直在这儿工作。 ② 用“it is/has been/will be + 时间段+ since”意为“自从?以来已多久了”。since从句应用非持续性动词的过去时。
It is/has been ten years since I began to learn English. 我学习英语已经10年了。
Next Month it will be six years since I came to Shanghai. 到下个月我来上海满6年了。 since的特殊用法
① 在 It is + 时间段 + since 结构中，since从句用持续性动词或状态动词的一般过去时， 意为“自从since表述的状态目前不存在以来，至今已有多长时间了”。
It is ten years since we lived here. 我们不住在这儿已经有 10 年了。
It is ten years since his father was a worker. 他父亲不当工人已经10年了。 How long is it since you were in Beijing? 你离开北京多久了？
② 主句现在完成时+since结构中，since从句用持续性动词或状态动词的一般过去时， 意为“自从since表述的状态 目前不存在以来，主句表述的 状况一直延续至今”。
The house has been in bad repair since they lived in it. 自从他 们搬出之后，这房子一直没有很好维修。
He has had several jobs since he was a student at Beijing University.从北京大学毕iL后，他已经干了好几份工作了。
③ 主句现在完成时+ since 结构中，since从句用持续性动 词或状态动词的现在完成时| 意为“ since从句的动作或状 态延续到说话时依然存在”。
I have often heard from him since he has lived in Shanghai. 自从他入住上海以来，我经常听到他的消息。
She has seldom been out since she has been ill. 自从她得病以来很少出门。
by the time:意为“到?时”，强调在某时前或到某时为止，主句动作已发生或某种情况已经出现，主句常用将来完成或过去完成时态。 by the time的用法
① by the time + 一般现在时 意为“到?的时候”。主句用将来完成时，有时也可以用将来完成进行时。
By the time he arrives, we will already have left California.
By the time he retires, he will have been working for fifty years. ② by the time + 一般过去时 主句常用过去完成时。
By the time he arrived, we had already gone. By the time I reached there, they had left.
By the time he got to class, the teacher had already started teaching.
③ by the time + 一般现在时/一般过去时 主句谓语动词表存在、拥有等的静态动词，如be，have, stay, 主句可用相应的一般式，不用将来完成式或过去完成式。
By the time you arrive, he will be in bed.
By the time we reached there, it was very dark.
By the time he died 1931, Edison had about a thousand inventions to his credit. By the time you arrive, we have stayed in Shanghai for ten years.
4) once, as soon as , instantly, immediately, directly 用于表示从句动作一发生，主句动
作随即发生。通常译为“一?就”。其中as soon as 比once 间隔的时间更短， instantly 表达随即发生的语气最强。 once 的用法 once 意为“一（旦）?就”，“只要”，可同时表时间和条件。
Once you see her, you’ll find what I say is true.
Once a good beginning is made , the work is half done. as soon as的用法
as soon as意为“一?就”，主要用于强调从句动作一发生，主句动作随即发生，两个动作间隔的时间很短。
I’ll go to see you as soon as I finish the work. I unpacked my bag as soon as I arrived. As soon as he had boiled the egg, he ate it.
They heard voices as soon as they pushed the door open. instantly等的用法 instantly, immediately, directly 意为“立即；顷刻；马上”，引出的从句发生在主句之前，用于表达间隔时间极短。
I knew something was wrong instantly I arrived. She recognized it immediately she saw it.
The policemen went into action directly they heard the alarm.
5) no sooner?than和hardly ... when,意为“刚?就”，表示一件事情紧接着 另一件事
情发生。no sooner/hardly引导的是主句,than/when引导的是从句。 no sooner ... than 的用法
① 此结构表示主句动作发生在从句之前，因此主句总是用过去完成时，从句用一般过去时。
hardly 可换用成 scarcely/ barely,when 可换用 before。
The sun had no sooner started to shine than it was clouded over again. I had hardly sat down when he stepped in.
The day had scarcely broken before he got up to work.
We had barely sat down before we heard someone shouting.
② 若把否定词No sooner或 Hardly/Scarcely/Barely 置于句首，主句中的主谓须倒装，时态仍用过去完成式。
No sooner had she sat down than the phone rang.
Hardly had I entered the room when I heard a loud noise. Scarcely had I opened the door when the dog came running in.
6）用下列time词组引导，表某一特定时刻发生或存在的情况。 the + 序数词 + time: the first time, the last time, the next time 不定代词 + time: every time，each time, any time time词组的用法 ① the first time, the last time, (the) next time表示特定时刻发生的事件或存在的情况。
I thought her nice and honest the first time I met her.
last time I tried that approach, things did not work out so well. Next time I see him, I'll show him my new dress.
② every time, each time, any time表示过去或现在特定情况下经常发生的事。
Each time you take a bite of food, chew at least 30 times before swallowing. Every time I went to his house, he was out.
说明：?The first time = when ...for the first time.例如：
I thought her nice and honest when I met her for the first time.
?whenever比each time, every time语气更强，多用于书面语。例如：
Whenever we met with difficulties, they came to help us. 7）用下列名词词组转化成时间连词引导从句，表示两个动作紧接着发生， 可译为“一?就”。
the + 时间点：the moment, the minute, the second, the instant the + 时间段：the morning, the day, the week, the year 表时间词组的用法
① the +表示时间点的瞬间名 词。意为“一...就”，“刚?就”
She came to the scene the moment she heard the news. I told him what we needed the minute I saw him. I recognized her the instant I saw her.
② the +表示时间段的名词，描述特定时间段里发生的事。
The morning he reached home, his grandfather died. The day her husband died, she gave birth to a son. They had a divorce the year they married.
2. 原因状语从句
原因状语从句表示主句动作或状态发生的原因或理由。主句表示结果，从句表示原因，主要由下列引导词引导:
because, since, as, for, seeing (that), considering (that) , now (that), in that, not ... because, not that ... but that 等
1) because “因为”，since “既然”，as“由于”，for“因为 because的用法
because表示直接的原因或理由，重点在从句，回答why，语气最强。可前置或后置。
He is absent today because he is ill.
Because you’re not burning calories, everything you eat turns to fat. since的用法
① since意为“因为”，用于附带说明，重点在主句。TOEFL考试认为必须前置。
Since he has no money, he can、buy a new car.
Since we live near the sea, we enjoy a healthy climate.
③ since意为“既然，由于”，表示据目前存在的情况进行推断，形成既成事实的理由，既表示原因，又有条件的含义。
Since you can’t answer the question, I’ll ask someone else. 既然你回答不出，我就问别人。 Since it can’t be helped, let us leave it at that. Since that is so, there is no more to be said. as的用法
as意为“由于”，表示对方已知的理由，仅作附加说明，TOEFL 考试认为须前置，多用于口语。
As it is snowing, we shall not go to the park.
this book is written in simple English, it is suitable for beginners. for的用法
① for意为“因为”是个并列连词，用于提供补充说明，常用于书面语，且只能置于句末，并用逗号或分号与主句分开。
I didn’t go to see him, for a heavy snow was falling. The days were short, for it was now December. He felt no fear, for he was very brave. ② 有时，for引起的从句只表示轻微的原因，主要为了强调主句的推断或对主句进行解释， 而because则不能。
He must be ill, for he is absent today. It is morning, for the bird is singing now.
He couldn’t have seen me that morning, for I was not there. 说明：介词短语because of, due to, owing to也表示原因，但是后面不能接句子。
He won’t be able to come because of the weather. 因为天气的缘故他不能来了。 He was unable to run due to a leg injury. 由于腿部受伤，他无法跑步了。 Owing to the rain, the match was canceled. 因为下雨，比赛取消了。 2）下列短语可用于引导原因状语从句。 seeing (that) “鉴于，既然”；considering (that) “考虑到”；now (that) “既然”； in that “因为”；not ?because“不是因为” ；not that ... but that “不是(因为)? 而是(因为)” seeing/considering that 的用法
seeing that “鉴于”与 considering that “考虑到”含义相近，所引导的句子中心在主句，重在强调该引起的结果。
Seeing that quite a few students were absent, we decided to put the meeting off. They did quite a good job considering that they had no experience. now that的用法 now that意为“既然”，表示由于新情况的出现而促成某件事情发生。
Now that he’d come to the door, he thought he might as well go in to have a look. Now that you’re grown up, you must stop this childish behaviour. in that的用法
in that意为“原因是，在于”， 用于正式文体。多指从一个或几个方面说明原因或理由，不能位于句首。
I like the city, but I like the country better in that I have more friends in the country. This book is unsatisfactory in that it lacks an index. 这本书并不令人满意，因为它少了个索引。
not ... because的特殊用法 意为“不是因为”。形式上not否定主句，含义上是否定because从句，从句前无逗号。也可将not直接放在because前。
She didn’t marry you because you had money. 她不是因为你有钱才嫁给你。 He did not come to the hospital because he wanted to see me. 他到医院来不是因为要看我。 not that ... but that 的用法 not that...but that, ( that = because),意为“不是因为?而是因为”解。该句型用作表语时不能改为 not because ... but because。
He felt worried, not that they were not working hard, but that they didn’t pay attention to safety.
The greatest tragedy of life is not that men perish, but that they cease to love.
人生最大的悲剧不是死亡，而是不再去爱。 威廉?毛姆
3. 地点状语从句
地点状语从句表示事件发生的地点或方向，由下列引导词引导: where, wherever, anywhere, everywhere 等 where的用法 ① where从句修饰主句的谓语动词，表示其运动或动作方向，意为“在...地方；到...地方”。
Make a mark where you have any doubts or questions. 在你有疑问的地方做个标记。 We will go where we are most needed. 我们要到最需要我们的地方去。
② where表示静止，用在be动词后 （这时，实际形成where引导的名词性从句作表语）或某些静态动词后， 意为“在?（所在的/原来的）地方”。
This is where you are wrong. 你错就错在这儿。
The car is where you put it. 汽车就在你原来停放的地 方。 It is safer to stay where you are.待在原来的地方会更加安全。
③ 将where置于句首，用于句型 “where there is ... , there is ... ”意为“哪里有?哪里就有?”，含有条件意义。
Where there is a will, there is a way. 有志者，事竟成。 Where there is water, there is life.有水之处就有生命。 ④ where表示对比，有抽象意义“在?地方”的含义。
Where others are weak, he is strong. 别人的弱点正是他 的强项。 Can you succeed where others failed. 别人失敗了，而你能成功吗？ wherever等的用法
① wherever意为“在任何?地方”，用于加强语气。
They went wherever they could find work.